This slipper is worked back and forth on straight needles holding two strands of yarn and working them as one.

The foot is worked in garter stitch and the toe is ribbed.

The heel and toe are seamed and a pompom decorates the
toe.

Back of heel seam: I use mattress stitch for garter, without a seam allowance by working right on the edge. When I get to the part that will go under the heel, I thread the needle through the sts and gather them up - just like I do for the toe closure.
At the bottom of the back/heel seam - I have also seamed this with 2 little horizontal seams that go perpendicular to the back seam, but I like this less.

Top of foot seam: if two knits come together, I work a mattress seam that uses the inner leg of each edge stitch. Work as invisibly as possible to make this version of mattress stitch without a seam allowance. I never use a whip stitch for this.